Officials are warning of a prolonged storm that’s set to hit the B.C. coast starting Sunday, which could lead to river levels increasing as the rain combines with snowmelt from warmer temperatures.

Environment and Climate Change Canada has issued special weather statements for the northern, western and inland sections of Vancouver Island, as well as the Central Coast, Howe Sound and the northern and northeast sections of Metro Vancouver on Friday.

Forecasters say a “prolonged atmospheric river event” will begin Sunday and last until at least Wednesday, with the heaviest rainfall expected Monday and Tuesday.

B.C.’s River Forecast Centre has issued high streamflow advisories for the entire B.C. coast on Friday, including the Fraser Valley and the Sunshine Coast, with up to 300 millimetres of rain forecast for western Vancouver Island and up to 120 millimetres in Metro Vancouver.

“There’s a pretty significant tropical storm … down in Hawaii, where they’re having some pretty heavy rainfall right now,” Jonathan Boyd, a hydrologist with the forecast centre, told CBC News.

“That is eventually going to make its way in this narrow band of, almost like a fire hose, hitting along the coast of B.C. for much of next week,” he added.

Boyd said it’s a bit too early to pinpoint exactly where the heaviest rain will occur.

But he said the storm will bring warmer temperatures with it, which could mean freezing levels — the height at which precipitation falls as snow, and not rain — will go up to at least 3,000 metres.

“That’s compared to the past week where freezing levels have been near sea surface levels … we have had some recent snow at low elevations all along the coast,” he said.

“So, it’s going to be a big shift.”

Potential for landslides

Environment Canada says there’s an enhanced risk of landslides due to water saturation that’s expected from the storm, along with the potential for flooding and washouts.

He said the warmer temperatures from the atmospheric river storm means that accumulated snow can melt, which could double the amount of water flowing into rivers and water bodies.

WATCH | What an atmospheric river is:

What is an atmospheric river?

It’s a term that became more widely known after record-setting flooding hit B.C. in November 2021, but as meteorologist Johanna Wagstaffe explains, atmospheric rivers are not new to west coast of North America.

He added the high streamflow advisories — the first step of a three-tiered flood warning system from the provincial forecast centre — could be upgraded to flood watches or flood warnings as forecasters get a more accurate read of the storm’s trajectory.

The hydrologist said that high streamflow advisories shouldn’t mean people take safety for granted.

“People go hiking and cross a small little creek in the morning, and by the time they have to come back in the evening, it’s now raging and moving very, very fast,” he said.

“Safety is paramount.”